Wind turbines provide an attractive means to produce renewable electricity at low costs. One of the key issues with power output from a wind turbine is its inherent intermittent nature, which often dictates that wind farms be augmented with supplemental generation capacity using natural gas firedturbines to enhance stability and dispatch ability of power supply.
Many inventors have sought a renewable energy solution that would provide a low cost stable and dispatchable power, without the use of fossil fuel. An extensive survey of patent literature has disclosed patents with this theme and these are summarized next.
U.S. Pat. No. 20100117372 (McMaster) discloses a “Hybrid Wind Turbine” where the shaft powerproduced by a wind turbine is integrated with shaft power produced from a thermal energy source like solar or fossil firing. The thermodynamic cycle employed for the thermal power source is a Rankine cycle utilizing a working fluid that changes phase. This system does not provide any means for renewable energy storage and dispatchability is maintained principally through fossil firing.
U.S. Pat. No. 2008029190 A1 (Sui) discloses a “Combined Wind Power Electricity Generator”, which is a hybrid wind turbine additionally powered by a gas jet during periods of insufficient windresource. The gas is stored in a gas bottle and is heated using solar heat. The exact mechanism for converting the gas or air jet into shaft power is not clearly detailed. Also there is no clear discussion of energy storage. The size as well as the practicality of the use of gas stored in bottles for utility scale applications is not addressed satisfactorily.
U.S. Pat. No. 4,229,941 (Hope) discloses a “Method and System for Generating Energy from Solarand Wind Resources”. The patent describes a solar thermal energy system utilizing a parabolic mirror and a Fresnel tube to produce steam. The steam is used to produce shaft power, which is integrated with the shaft power produced by wind. The system described in this patent is more suited to residential applications and its scalability to utility scale is questionable. Also this system does not address the question of energy storage.
U.S. Pat. No. 4,229,941 (Enis) discloses a method in which power generated from a single or multiple windmills is stored as compressed air in a single or multiple pressurized storage tanks. During times when wind is not available, the compressed air is converted into power via a turbo exchanger.
Heat is added to compressed air utilizing several sources of energy such as: solar thermal, waste heat collector and a separate heating unit. This system provides means for renewable energy storage and dispatchability through compressed air storage system, which requires high volume storage tanks at high-pressure.
U.S. Pat. No. 7,851,935 (Tsao) discloses a method in which a parabolic dish/trough solar collector is interconnected to a thermo-mechanical engine. The thermo-mechanical engine is mechanically integrated to the transmission element of the wind turbine through a secondary shaft. The system was designed as a small-scale roof top system. The storage element in their system is purposed to store direct electricity.
U.S. Pat. No. 7,615,884 (McMaster) discloses an enhancement to an existing wind turbine. The enhancement is done using an auxiliary power section, which is connected to the generator to enable longer time periods in which the wind turbine generator can be utilized. The generator itself has two inputs, one from the primary power generation, i,e, the wind turbine rotor and a secondary one from the auxiliary section, where each one of the inputs can drive the generator independently. The described system has three modes of operation: wind only, auxiliary only and combined. The auxiliary powersection can be one of many of heat engines such as: combustion engine, gasoline engine, diesel engine, natural gas etc. The heat recovery (recuperation) system uses the exhaust heat from the heat engine as well as the solar collector system to heat a liquid medium. The liquid medium can either be water, which will be used directly through a steam turbine (as one form of an auxiliary motor options) or as a liquid source to an organic Rankine turbine (as another form of an auxiliary motor), where it will be recycled back to the solar absorber. No storage of any type has been included in this system.